Method of manufacturing polyvinyl alcohol fiber of improved property

ABSTRACT

THE PROPERTIES OF POLYVINYL ALCOHOL FIBERS ARE IMPROVED BY SPINNING POLYVINYL ALCOHOL CONTAINING BORIC ACID OR A BORATE INTO AN ALKALINE SPINNING BATH CONTAINING A CONVENTIONAL DEHYDRATING SALT AND AN ADDITIVE COMPRISING 4X10**-5 TO 9X10**-2 MOL/L. OF (A) AN AMINOPOLYCARBOXYLIC ACID, OR (B) A CONDENSED PHOSPHORIC ACID, OR (C) A SALT, E.G., SODIUM OR POTASSIUM OR AMMONIUM SALTS OF (A) OR (B).

1973 YOSHIHIDE YOSHIOKA ET L I METHOD OF MANUFACTURING POLYVINYL ALCOHOL FIBER OF IMPROVED PROPERTY Filed Nov. 26, 1971 EXAMPLE I COMPARATIVE EXAMPLE I 65 5325125 zoom E E925 @z wmm E0 DAYS AFTER SPINNING \NVENTORS YOS'HIHIDE YOSHIOKA SHIGEKAZU KOBAYASHI AKIO MIZOBE United States Patent O METHOD OF MANUFACTURING POLYVINYL ALCOHOL FIBER OF IMPROVED PROPERTY Yoshihide Yoshioka, Saijo, and Shigekazu Kobayashi and Akio Mizobe, Kurashiki, Japan, assignors to Kuraray Co., Ltd., Kurashiki, Japan Filed Nov. 26, 1971, Ser. No. 202,384 Claims priority, application Japan, Nov. 27, 1970, 45/ 105,374 Int. Cl. D0111 1/10 US. Cl. 264-170 13 Claims ABSTRACT OF THE DISCLOSURE The properties of polyvinyl alcohol fibers are improved by spinning polyvinyl alcohol containing boric acid or a borate into an alkaline spinning bath containing a conventional dehydrating salt and an additive comprising 4X10 to 9 x10 mol/l. of (a) an aminopolycarboxylic acid, or (b) a condensed phosphoric acid, or (c) a salt, e.g., sodium or potassium or ammonium salts of (a) or (b).

BACKGROUND OF THE INVENTION The present invention relates to a method of wet spinning polyvinyl alcohol (hereinafter abbreviated as PVA) fiber that contains boric acid or a borate and to spinning and manufacturing with high stability a 'PVA fiber of high strength and high modulus.

It is generally known that a PVA fiber can be produced by spinning a PVA spinning solution containing boric acid or a borate into an alkaline coagulation bath. For example, Japanese patent publication Nos. 8,918/ 1956 and 2,061/ 1959 disclose a method of spinning a =PVA spinning solution containing boric acid or borate into an alkaline coagulation bath containing various salts. In this method, it is assumed that a fiber is formed by the PVA spinning solution making a gelatinizing reaction with the alkaline ingredients of the coagulation bath, a dehydro-coagulating reaction with the salt, and a cross linking reaction between PVA and boric acid in the fiber. By the reason that such reactions are elfected simultaneously, the spinnability of the solution is very delicate and even a slight change in conditions makes spinnability extremely unstable, with the result that there are observed considerable discrepancies in quality of the fibers obtained, especially deterioration in quality with the lapse of time.

As stated above, the spinning method of the type described above has been known for some time, and basic studies have been extensively made of the method. Accordingly, it is reported that the method can now provide a fiber of improved properties, but nevertheless it is certain that spinnability difficulties and instability of quality of the fibers have constituted some of the reasons that have so far hampered the industrial application of the method.

SUMMARY OF THE INVENTION The present inventors, in an effort to inquire into the factors causing instability of spinnability and properties of the fibers, particularly in conjunction with changes in the properties and the spinnability with the lapse of time, have found that scales adhered adjacent to the spinning nozzle holes form a main factor in the problem, and they have further found that the scales comprise metal salts such as iron and calcium salts.

Accordingiy, the inventors discovered that it is necessary to prevent the growth of such scales in order to stabilize the spinnability and properties of the fiber, and have worked out the present invention after various researches.

Namely, the method of the present invention is the one of producing a PVA fiber of improved property by spinning of a PVA spinning solution containing boric acid or borate into an alkaline coagulation bath containing 4x10 to 9X10 mol/l. of a compound selected from aminopolycarboxylic acid or sodium and potassium salts (hereinafter abbreviated as salts thereof), and condensed phosphoric acid or sodium, potassium and ammonium salts (hereinafter abbreviated as salts thereof).

According to the present invention, the formation of scales is completely prevented by spinning in the presence of 4X 10* to 9 x 10- mol/l. of a compound selected from aminopolycarboxylic acid or its salts, and condensed phosphoric acid or its salts in an alkaline coagulation bath. The spinnability is highly stabilized with the result that the fiber obtained is entirely free from deterioration in quality due to lapse of time and has become well adapted for production on an industrial basis. When an aminopolycarboxylic acid, a condensed phosphoric acid or a salt thereof is not added, spinnability of the spinning solution got worse as time passed after the start of spinning, and the fiber obtained also has poor properties and the service life of the nozzle was at most less than five days. But the present invention makes it possible to spin with stabilized effectiveness for more than fifteen days, and also deterioration in the properties of the fiber obtained due to time lapse in the meantime is prevented.

Furthermore, it was found that the method of the present invention could produce a fiber far superior in such properties as strength, and initial modulus t0 the fiber produced from a coagulation bath to which aminopolycarboxylic acid, condensed phosphoric acid or a salt of either of these acids was not added.

It seems that the reason why the proposed method prevents the adhesion of scales adjacent to the nozzle holes is ascribable to formation of a stable chelate produced by reaction between aminopolycarboxylic acid, condensed phosphoric acid or salt thereof with metal ion such as calcium, and iron ion, present in the coagulation bath.

The reason of acquisition of excellent property of the fiber is not yet fully known, but the aminopolycarboxylic acid, condensed phosphoric acid or salt thereof present in the coagulation bath produces a direct or indirect effect upon the dehydration and gellation of PVA spinning solution containing boric acid or borate, thereby producing a compact and fine microstructure in the PVA fiber.

While the above theories are offered by way of explanation, it is not intended to be in any way bound or limited by their veracity.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying sheet of drawing, the single figure therein shows a difference in the change caused by lapse of time in the dry breaking tenacity at room temperature between polyvinyl alcohol synthetic fibers provided according to the method of the present invention and according to conventional methods.

DETAILED DESCRIPTION OF THE INVENTION The PVA used in the invention has a degree of polymerization of more than 500 and a degree of saponification of more than 98% (mol), preferably more than 99% (mol). The spinning solution has a PVA concentration of preferably 10-30% by weight of aqueous solution, contains 0.55% by weight of boric acid or borate, and has a pH of 3.56.

The coagulation bath into which the PVA spinning solution is spun is an aqueous solution containing 5-200 g./l. of caustic alkali and 100 g./1. saturating concentration of a salt capable of dehydration in addition to aminopolycarboxylic acid, condensed phosphoric acid or salt thereof. In this connection, sodium hydroxide or potassium hydroxide is used as caustic alkali, and sodium sulfate, ammonium sulfate, sodium carbonate, is used as the salt being capable of dehydration.

The most desirable aminopolycarboxylic acid or its salts used in the invention are ethylenediaminetetraacetic acid and its mono-, di-, trior tetra-sodium salts or mono-, di-, tri-, or tetra-potassium salts and nitrilotriacetic acid and its mono-, di-, or tri-sodium salts, and mono-, di-, or tripotassium salts. In addition there may be used trimethylenediaminetetraacetic acid, methylaminediacetic acid, 1,2-cyclohexylaminetetraacetic acid, and their sodium or potassium salts.

Condensed phosphoric acids useful in the invention include polyphosphoric acids having a general formula of H P O wherein n is 2-100, and preferred examples are pyrophosphoric acid (11:2), triphosphoric acid (n=3) tetraphosphoric acid (n=4), salts thereof, and Grahams Salt (11:30-90). Another class of useful condensed phosphoric acids comprise polymetaphosphoric acids having a general formula of (HPO wherein n is 3-10, and preferred examples are trimetaphosphoric acid (11:3), tetrametaphosphoric acid (11:4), hexametaphosphoric acid (11:6), and salts thereof. A further class of useful condensed phosphoric acids comprises ultraphosphoric acids having a general formula of xH O-yP O wherein x/y is greater than and less than 1, and preferred examples are 2H O-3P O In the method of the present invention, the novel additive compound is added to a coagulation bath in the form of the acid or salt thereof and it is especially important to maintain its concentration within the specific range of 4X10- 9 10- mol/l. as shown in the following examples.

The term salt when used in reference to a salt of aminopolycarboxylic acid or of a condensed phosphoric acid is used in a broad sense to include a chelate compound, and thus this term includes a salt of an aminopolycarboxylic acid or of a condensed phosphoric acid with a metal having a smaller chelate formation constant than magnesium ion. Thus salts of sodium, potassium, and silver which are smaller in chelate formation constant than magnesium are included within this definition, and salt of iron, calcium, and copper which have larger chelate formation constants than magnesium are not included within this definition.

The concentration of either aminopolycarboxylic acid, or condensed phosphoric acid, or salts of the above in the coagulation bath is 4X to 9 10- mol/1., preferably 1.7 10- to 1.7 10- mol/l.

When the concentration is lower than 4 10- mol/1., the intended effect of the invention cannot be obtained, and when the concentration is higher than 9 10- mol/1., the coagulating property of PVA spinning solution is reduced and hence PVA fiber of improved properties cannot be obtained.

In the invention, spinning of a PVA spinning solution containing boric acid or borate into an alkaline coagulation bath containing aminopolycarboxylic acid, condensed phosphoric acid or salts thereof can be carried out in accordance with an ordinary wet spinning method. The fibers obtained can be further subjected to neutralization with acid, washing with water, drying, drawing, heat treatment and acetalizing treatment.

The PVA fiber obtained by the invention has excellent strength and initial modulus particularly at high temperatures, and is especially well suited for use as an industrial material in making tires and belts that are used under severe conditions.

The invention will now be described below by the examples. The dry breaking tenacity and initial modulus shown in the examples are measured as follows.

Dry breaking tenacity: This is a value of a sample fiber 20 cm. long being twisted 8 turns/ 10 cm. then dried for 3 hours at 105 C., measured in accordance with the Japanese Industrial Standards L 1070 by a tensile testing machine (constant rate of extension type) in which an elastie film (Lycra film made by Du Pont Company) is stuck to the jaw face of a chuck, and drawing the sample at a drawing speed of 10 cm. per minute.

Initial modulus: This is a value measured on the basis of the stress-strain curve obtained by measuring the foregoing dry breaking tenacity in accordance with Japanese Industrial Standards L 1073. When the measurement is made at normal temperature, it is made in a room maintained at 20 C. and when the measurement is made at high temperatures, it is made by setting an electric heater so that the upper and lower chucks and the sample are maintained at C.

Example 1 A hundred kg. of PVA having a polymerization degree of 1,700 and a saponification degree of 99.9 mol percent were dissolved in water to obtain an aqueous solution containing 16 weight percent of PVA, and a spinning solution was prepared from the aqueous solution by adding 2.5 kg. of boric acid (2.5% by weight to PVA), and tartaric acid so as to obtain a pH of 4.5.

This spinning solution was extruded into a coagulation bath through a nozzle having 1000 holes each 0.06 mm. in diameter at an extrusion rate of 150 g. per minute and the product was removed from the bath at a speed of 8 111. per minute. The coagulation bath contained 100 g./l. of sodium hydroxide, 150 g./l. of sodium sulfate, and 3.4 10 mol/l. of disodium ethylenediamine tetraacetate measured by titration with magnesium chloride.

Subsequently, the spun fiber was drawn with rollers at a ratio of 100%, thereafter sodium hydroxide adhered to the fiber was neutralized with sulfuric acid. Then the resulting fiber was wet hot drawn at a ratio of 100%, washed with water, dried, dry hot-drawn at a ratio of 250%, heat treated, taken up, and thereafter the properties of the fiber were measured.

Control Example 1 Aside from the fact that no disodium ethylenediamine tetraacetate was added to the coagulation bath, the treatment was essentially the same as that of Example 1. The results of Example 1 and Control Example 1 are shown in Table I and FIG. 1.

1 Stable for 15 days. 1 Decreased from 5th day. 8 See FIG. 1.

Examples 2-5 and Control Examples 2-3 A hundred kilograms of PVA having a polymerization degree of 1750 and a saponification degree of 98.5% were dissolved in water to obtain an 18% by weight aqueous solution, and a spinning solution was prepared by adding to the above solution 2.0 kg. of boric acid (2.0% by weight to PVA) and tartaric acid to obtain a pH of 4.0.

This spinning solution was spun through a nozzle having 800 holes each 0.10 mm. in diameter at an extrusion rate of g./min. into an aqueous coagulation bath to which 10 g./l. of sodium hydroxide, 500 g./l. of ammonium sulfide, and tetrasodium ethylenediamine tetra acetate were added, and the resulting fiber was removed from the bath at a speed of 8 m. per minute.

By changing the amount of tetrasodium ethylenediamine tetraacetate added to said coagulation bath, the concentration of ethylenediamine tetraacetate that can be quantitatively determined by magnesium chloride was 7 10- mol/l. (Example 2), 1.7 10 mol./l. (Example 3), 1.7 10- mol./l. (Example 4), 5x10" mol./l. (Example 2 1-0- mol/l. (Control Example 2) and 12 10- mol/l. (Control Example 3).

The spun fiber was subjected to a drawing ratio of 100% by rollers, and thereafter the adhered sodium hydroxide was neutralized. Then the resulting fiber was wet hot-drawn by 100%, washed with water, dried, and then dry hot drawn by 250%, heat treated and taken up on a bobbin.

The details of the spinning operation and the resultant quality of the spun yarn are shown in Table II.

1 day... Initial modulus at room temperatnre(g./d.) 275 290 283 272 230 Initial modulus at high temperature 1 Stable for 15 days. 1 Decreased from 5th day. 3 Decreased from 11th day.

Example 6 Instead of using disodium ethylenediamine tetraacefate in the coagulation bath as in Example 1, trisodium nitrilotriacetate was added in an amount of 3.4 10- mol/l. measured by the titration with magnesium chloride. The treatment was otherwise essentially the same as that of Example 1. The results of the spinning thus effected are shown in Table III.

Control Example 4 Aside from the fact that the concentration of 3.4x l0" mol/l. of the trisodium nitrilotriacetate in Example 6 was substituted by 12 10- mol/1., spinning was carried out under the same conditions as in Example 6. The results obtained are shown in Table III in comparison with the results of Example 6.

\ Stable for 15 days. 2 Decrease from 9th day. v

Example 7 100 kg. of PVA having a polymerization degree of 1,700 and a saponification degree of 99.9 mol percent were dissolved in water to form an aqueous solution containing 16 weight percent of PVA,, and a spinning solution was prepared from the aqueous solution by adding 2.5 kg. of boric acid (2.5% by weight to PVA) and tartaric acid in an amount to obtain a pH of 4.5. This spinning solution was extruded into a coagulation bath through a nozzle having 1000 holes each 0.06 mm. in diameter at an extrusion rate of 150 g./min., and removed from the bath at a speed of 8 ml. per minute. The coagulation bath contained 100 g./l. of sodium hydroxide, 150 g./l. of sodium sulfate, and 2X10" mol/l. of triphosphoric acid. Subsequently, the spun fiber was drawn with rollers at a ratio of 100%. Thereafter, the sodium hydroxide adhered to the fiber was neutralized with sulfuric acid. Then the resulting fiber was wet hot-drawn at a ratio of washed with water, dry hot-drawn at a ratio of 250%, heat treated, taken up on a bobbin. Thereafter the properties of the fiber were measured.

Control Example 5 Aside from the fact that no triphosphoric acid was added to the coagulation bath, the treatment was essen tially the same as that of Example 7. The results of Example 7 and Control Example 5 are shown in Table IV:

TAB LE IV Control Example 7 Example 5 Spinnability Fiber-breaking in drawing (times/100 kg.) 0. 3 6. 3

Dry lbireaking tenacity at room temperature lst d ay 10. 9 9. s 10.9 9. 3 11.3 8. 5 l1. 1 y 10. 9 Initial modulus at room temperature 285 240 Initial modulus at a high temperature (g./d.) 150 100 1 Stable [or 15 days. 2 Decreased from 5th day.

Examples 8-11 and Control Examples 6-7 100 kg. of PVA having a polymerization degree of 1750 and a saponification degree of 98.5% was dissolved in water to obtain an aqueous solution containing 18 wt. percent PVA, and a spinning solution was prepared from the aqueous solution by adding 4.0 kg. of boric acid (4.0% by weight to PVA) and suflicient tartaric acid to bring the pH to 4.0. This spinning solution was extruded into a coagulation bath through a nozzle having 800 holes each 0.10 mm. in diameter at an extrusion rate of g./min., and the fibers were removed from the bath at a. speed of 8 m. per minute. The coagulation bath contained 10 g./l. of sodium hydroxide, 500 g./l. of ammonium sulfate, and sodium tetraphosphate. By changing the amount of sodium tetraphosphate added to the coagulation bath, baths were prepared containing the following amounts of sodium tetraphosphate: 7 10* mol/l. (Example 8), 1.7 10- mol/l. (Example 9), 1.7 10" mol/l. (Example 10), 5X10 mol/l. (Example 11), 5 X 10- mol/l. (Control Example 6), and 5 X 10* mol/1. (Control Example 7) respectively. The spun fibers were subjected to a drawing ratio of 100% by rollers, and thereafter the adhered sodium hydroxide was neutralized. The resulting fibers were wet hot-drawn by 100%, washed with water, dried, dry hot-drawn by 250%, heat treated and taken up on bobbins. Spinnability and the properties of the fibers are shown in Table V.

10 Dry bleaking tenacity at room teingieg'ature (g./d.):

Initial modulus at room mperature (g./d.) 285 300 290 280 210 220 Initial modulus at high temperature 1 Stable for 15 days. 2 Decreased from 5th day. 5 Decreased from 11th day.

Example 12 Instead of using triphosphoric acid in the coagulation bath as in Example 7, sodium hexametaphosphate was added to the bath in an amount of 3.4 10- mol/1., and spinning was carried out under the same conditions as in Example 7. The results obtained are shown in Table VI.

7 Control Example 8 TABLE VI Control Example 12 Example 8 Spinnability Fiber breaking in drawing (times/100 kg.)

Dr('y llreaking tenacity at room temperature 1st day 4th day.- 7th day th day.

th day. Initial modulus at room temperature (gt/d.) Initial modulus at high temperature (g./d.)

1 Stable for 15 days. I Decreased from 9th day.

What is claimed is:

1. In a method of producing a polyvinyl alcohol fiber comprising:

(1) wet-spinning an aqueous polyvinyl alcohol spinning solution containing from about 0.5 to 5% by weight, based on the weight of polyvinyl alcohol, of boric acid or a borate into an alkaline coagulating bath containing (a) from about 5 to 200 g./l of solution of an alkaline compound and (b) from about 100 g./l. of solution to an amount necessary to saturate said coagulating bath of a dehydrating salt;

(2) neutralizing the resulting fiber with an acid;

(3) washing the fiber with water;

(4) drying the fiber;

(5) drawing the fiber; and

(6) heat-setting he fiber, the improvement comprising improving the spinnability of said spinning solution and producing a polyvinyl alcohol fiber having increased strength and initial modulus by wet-spinning said spinning solution into a coagulating bath consisting essentially of, in addition to said (a) and (b), from about 4X10 to 9 l0- mole/liter of solution of a compound selected from the group consisting of an aminopolycarboxylic acid, a condensed phosphoric acid and salts thereof.

2. A method according to claim 1, wherein said compound is selected from the group consisting of ethylenediaminetetraacetic acid and its mono-, di-, trior tetrasodium salts or mono-, di-, trior tetra-potassium salts; nitrilotriacetic acid and its mono-, di-, or tri-sodium salts, and mono-, di-, or tri-potassium salts; and trimethylenediaminetetraacetic acid, methylaminediacetic acid, or 1,2- cyclohexylaminetetraacetic acid, and their sodium or potassium salts.

3. A method according to claim 1, wherein the salts of said compound are the sodium, potassium or ammonium salts thereof.

4. A method according to claim 2, wherein said compound is selected from the group consisting of: (1) polyphosphoric acids of the formula H P O wherein n is 2-100; (2) polymetaphosphoric acids of the formula (HPO wherein m is 3-10; (3) ultraphosphoric acids of the formula xH O-yP O wherein x/y is greater than 0 but less than 1; and (4) the sodium, potassium or ammonium salts thereof.

5. A method according to claim 1 wherein the polyvinyl alcohol has a degree of polymerization of more than 500 and a degree of saponification of more than 98 mole percent.

6. A method according to claim 1 wherein the concentration of the polyvinyl alcohol in said spinning solution is from 10 to 30% by weight, based on the weight of the spinning solution, and wherein the pH of said spinning solution varies from 3.5 to 6.

7. A method according to claim 4 wherein said polyphosphoric acid is selected from the group consisting of pyrophosphoric acid wherein n is 2, triphosphoric acid wherein n is 3, tetraphosphoric acid wherein n is 4 and Grahams Salt wherein n varies from 30 to wherein said polymetaphosphoric acid is selected from the group consisting of trimetaphosphoric acid wherein m is 3, tetrametaphosphoric acid wherein m is 4 and hexametaphosphoric acid wherein m is 6; and wherein said x and said y in the general formula for said ultraphosphoric acid are 2 and 3, respectively.

8. A method according to claim 4, wherein the amount of said compound in said coagulating bath is from about 1.7 10- to 1.7 10 mole/l. of solution.

9. A method according to claim 4, wherein the fibers are further subjected to an acetalizing treatment after said heat-setting treatment.

10. A method according to claim 1 in which said compound is an aminopolycarboxylic acid and is present in said coagulating bath in a concentration of from about 1.7 10- to 1.7 l0- mole/l. of solution.

11. A method according to claim 1 in which said compound is a condensed phosphoric acid and is present in said coagulating bath in a concentration of from about 1.7 10- to 1.7X' mol/l. of solution.

12. A method according to claim 1, wherein said alkaline compound is selected from the group consisting of sodium hydroxide and potassium hydroxide.

13. A method according to claim 12, wherein said dehydrating salt is selected from the group consisting of sodium sulfate, ammonium sulfate, and sodium carbonate.

References Cited UNITED STATES PATENTS 2,888,318 5/1959 Parker 264169 2,345,570 4/1944 Bley 264170 2,648,592 8/1953 Stanton et al. 8--137.5 2,648,593 8/1953 Stanton et al 8137.5 2,904,391 9/1959 Bennett et al 8137.5 3,003,993 10/1961 Wooten 8-137.5 3,415,611 12/1968 Callahan et a1 8-137.5 3,156,667 11/1964 Martins 260-913 UA 3,210,147 10/1965 Johnson et al. 260-913 UA 3,660,556 5/1972 Ashikaya et al. 264-485 FOREIGN PATENTS 22,770 9/ 1969 Japan 2641 85 JAY H. WOO, Primary Examiner US. Cl. X.R. 264-l69, 

